Mach's principle and local Lorentz invariance together yield the prediction of rest mass fluctuations in objects that are accelerating and simultaneously undergoing changes in their internal energy states. These rest mass fluctuations, both in principle and in practice, can be quite large and, in principle at least, negative. They suggest that exotic spacetime transport devices may be feasible, the least exotic being “impulse engines”, devices that can produce accelerations without ejecting any material exhaust. Such “impulse engines” rely on inducing mass fluctuations in conventional electrical circuit components and combining them with a mechanically coupled pulsed thrust to produce propulsive forces without the ejection of any propellant. One simply pushes on the circuit component in which the rest mass fluctuation is induced when it is more massive than average, and pulls back on the component when it is in a mass reduced state, the result of these actions being a net time-averaged force directed away from the fluctuating rest mass component. This method of producing thrust with force transducers (ferroelectric devices or their magnetic equivalents) attached to resonant mechanical structures is already described in U.S. Pat. Nos. 5,280,864; 6,098,924: and 6,347,766. In the method described therein, and in other published work, ferroelectric force transducers, in particular, piezoelectric transducers, are driven by two (or more) phase-locked voltage waveforms so that the rest mass fluctuation and mechanical excursion needed to produce a stationary thrust are both produced in the transducer itself.